Pancreatic islets

Function

A million islets of Langerhans — 1–2% of pancreatic mass — run the body's glucose economy. Beta cells (70%) secrete insulin within minutes of a meal's glucose rise, opening cells to glucose uptake; alpha cells (20%) secrete glucagon in fasting to release stored glucose; delta cells pace the pair with somatostatin.

Each islet is a micro-organ: its own capillary wreath drains hormones straight into the portal vein, giving the liver first audience — 50% of portal insulin is extracted there before the systemic blood ever sees it.

Blood supply

Branches of the splenic and pancreaticoduodenal arteries; each islet has a dense capillary network.

Nerve supply

Vagal cholinergic input sharpens insulin release; sympathetic adrenaline suppresses it (the fight-or-flight hyperglycaemia).

Clinical relevance

Type 1 diabetes

Autoimmune beta-cell loss — insulin dependency from diagnosis, usually in youth.

Type 2 diabetes

Islet beta-cells exhaust against insulin-resistant tissues; glucagon's excess adds to the hyperglycaemia.

Insulinoma

A rare beta-cell tumour — hypoglycaemic episodes relieved by eating, diagnosed by supervised fasting.

Related conditions

• Type 2 diabetes
• Type 1 diabetes